Reduced Ow/Reduced Pressure - Danfoss PAHT Operation, Installation, And Maintenance Manual

Operation guide
2.

Reduced ow/reduced pressure

Cause
2.1 Wear on pump
Large internal leakage due to:
2.2 Low inlet pressure
2.3 Rotation speed (rpm)
© Danfoss | 2023.12
Installation, Operation and Maintenance Manual for PAHT 20-90 pumps
Remedy
2.1.1 Dismantle the pump.
2.1.2 Check valve plate.
Valve plate has marks/scratches on the
surface facing the port plate. Minor wear
on valve plate can cause large internal
leakage. See Index 6.1.
2.1.3 Check port plate.
Port plate has marks/scratches on the
surface facing the valve plate. Minor wear
on port plate can cause large internal
leakage. See Index 6.2.
2.1.4 Check cylinder barrel.
Liners in cylinder barrel may be scratched
or worn. Insert a piston in the liner and
check the t. If there is any space (clear-
ance) between liner and piston, liner or
piston is worn.
2.1.5 Pre-treatment:
Analyse uid for content of particles.
- Check that lters are OK and working
correctly.
2.1.6 Main ltration:
Check that the correct lter type is used
(particles in uid must not exceed 10 m).
Danfoss High Pressure Pumps supplies
lters, please contact the sales o ce.
2.1.7 Fluid type:
The PAH/PAH F (tapwater) and PAHT/PAHT
G (ultra pure water) pumps are designed
for water operation; for any other uid,
please contact Danfoss High Pressure
Pumps sales o ce for further help.
2.1.8 High uid temperature:
If uid temperature is above 50°C, stop the
pump immediately.
- Check internal parts (see above).
2.2.1 Check that booster pump supplies the
right pressure/ ow.
2.2.2 Check if lters require replacement.
2.3.1 If VFD-operated, check frequency.
2.3.2 Check that rotation speed of the electric
motor is as stated on name plate on
electric motor. Check that the motor rotor
winding is not damaged.
Comments
Typical signs of wear:
Polished surface all over the swash plate.
Normally, only half of the swash plate = the
pressure side is polished. See index 6.3.
If the ring is missing, the piston is very worn.
The lters can be bypassed, even if they are
correctly mounted. Some lters can create
channelling where particles can pass through
the lter in tunnels. String wounded lters are
typically channelling lters. A string wound lter
may have a ltration e ciency of only 50%,
which will cause internal wear and must always
be followed by a main lter.
Insu cient ltration means that too many or too
large hard particles can pass the main lter
because it is damaged, bypassed or simply too
poor. Filtration e ciency must be 99.98%
(Beta = 5000) at 10 m to prevent abnormal
wear of the pump.
Temperature > 50° C will cause wear on internal
pump parts. Mount a temperature switch and
check its set point / function. The temperature
switch will ensure that the pump stops at uid
temperatures > 50° C.
If the pressure drop across the lters is too high,
the booster pump does not deliver su cient
ow/pressure. No pressure or low pressure
results in cavitation and insu cient internal
lubrication causing wear on internal pump parts.
Mount a low-pressure switch in front of the
pump and check its set point/ function. The
low- pressure switch ensures that the pump does
not start until the inlet pressure has reached 1
bar.
Speeds below minimum limit (see Data sheet)
result in insu cient internal lubrication causing
wear on the internal pump parts.
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